14 



The reduced infection in the growth-chamber experiments and the 

 reduced lesion length in the greenhouse experiments were due to the 

 partial restabilization of the treated soil and root environment "by the 

 addition of the antagonists. The observation that nearly all of the 

 plants were infected, including the controls, in the greenhouse studies 

 was attributed to the long duration (12 wk) of the experiment and the 

 ability of the pathogen to spread as airborne inoculum. Rowe et al. 

 (28) found that under greenhouse conditions treated soil was rapidly 

 reinfested by the pathogen as airborne micro conidia. 



The success of reducing the severity of Fusarium crown rot of 

 tomato with biological control is dependent upon the reestablishment in 

 freshly treated soil of a microbial community that impairs the rein- 

 vasion by F. oxysporum f . sp. radicis-lycopersici . The host-pathogen 

 model employed in this study allowed the development of a system for the 

 selection of antagonists and the quantification of a biological control 

 procedure under growth-chamber and greenhouse conditions. This infor- 

 mation provides qualitative and quantitative bases for the application 

 of antagonists in the field in south Florida. In addition to the field 

 experiments, information is needed on the effects of the addition of 

 antagonists on recolonization by artificially and naturally introduced 

 microorganisms. The interactions of several microbial populations can 

 best be understood at the community level of the ecosystem and therefore 

 the concepts of community stability and succession will be applicable to 

 future studies on the quantification of biological control . 



